This invention relates to an iontophoresis electrode for applying medicaments to the human body by applying electrical current in an effort to produce a desired reaction or effect. More specifically, the invention relates to an electrode that can be used in iontophoresis applications which is constructed of a polyvinyl chloride (PVC) or similar material and has a barrier layer to prevent plasticizer from migrating from the PVC or similar material into the conductive portion of the electrode.
Electrical current can be applied to the human body for many different purposes. For example, electrical current is commonly used in iontophoresis where drugs are delivered to the human body in a very controlled manner. In this application, the electrical current is applied to medicaments and they are delivered in a controlled manner to the human body in this manner. The level and duration of current supplied directly controls the amount of medication provided. Several controllers and systems exist for iontophoresis. The concept of iontophoresis is very well known to those skilled in the art.
As with any electrical system in which an electrical current is to be applied to the human body, the risk of electrical burns can exist. These electrical burns typically result from too much electrical charge being applied to the body--either through large amounts of current, or through prolonged application. It goes without saying that these burns need to be prevented, and close controls must be in place to insure that they do not occur. These controls include closely monitoring the systems that are being used, as well as monitoring all of the component. In this way, unexpected results can be prevented.
In order to have the electrical current applied to the desired drug reservoir, the electrodes preferably have a conductive layer which is attached to the current producing circuit. The conductive layer is configured to be adjacent the drug reservoir, and backed by some insulating material. One such configuration includes a foam backer with a carbon layer attached thereto. Also adjacent the carbon layer, opposite the foam backer, is the required drug reservoir. This carbon layer then provides the necessary conductivity to activate the drug delivery mechanisms.
In most iontophoresis systems, the electrodes are manufactured so as to be conformable to the body, while also having the desired electrical characteristics. In many medical applications, PVC films are used because of their softness and conformity. These films could work well in electrodes as the foam backing element because they would be capable of easily conforming to the body of the patient. Despite this potential advantage, PVC has a tendency to leach plasticizers into surrounding media. This is particularly problematic in the context of medical electrodes because this leaching can alter the electrical characteristics of the conductive materials. As can be appreciated, the uncontrolled change of an electrode's electrical characteristics can result in the undesired application of electrical current to the body, and possibly burns.
In the context of iontophoresis systems, changing the formulation of the material from which the backing layer was formed and/or crosslinking of the plasticizers with each other or the other components of the material and/or adhesive have been attempted without commercial success. Alternatively, the conductive layer of the electrode is constructed of material such as from foil, felt, or gauze formed of metal such as aluminum or stainless steel, which have little transference of plasticizers. However, because of increased burn risks, especially for metal conductive layers, electrodes of these types can only be used for short times.
Further, numerous other mechanisms have been attempted to control the characteristics of the electrodes. For example, U.S. Pat. No. 5,840,056 to Antanasoska provides an electrode having an incorporated pH buffer. This pH buffer is specifically configured to scavenge undesired H+ or OH-(hydrogen and hydroxide) ions created by the electrolysis of water. Similarly, U.S. Pat. No. 4,973,303 to Johnson et al. provides a buffered electrode in which a pH buffer is incorporated to again provide the scavenging function.
Another solution is provided in U.S. Pat. No. 4,886,489 where a flushing type action is used. In this system, a flushing compound is circulated through the electrode. In use, all undesired ions have been swept away in the circulating compound.
Another way to control the electrical current being applied to the patient is through control of the electrical supply circuit. It is recognized that many different type of circuits could be configured to provide the desired electrical signals. One such system which could be used for producing the necessary signals is described in U.S. Pat. No. 5,431,625 entitled Iontophoresis Electronic Device Having Ramped Output Current. U.S. Pat. No. 5,431,625 provides much more detailed description of such a circuit, and is herein incorporated by reference.